Spatial Relationships for Vegetation in Restored and Reference Salt Marshes in the Salmon River Estuary, Oregon

Graduation date:2017In this thesis, the spatial patterns of vegetation and soils of reference and \ud restored tidal marshes were compared to determine the extent to which restored sites \ud differ from the reference site after 40 years of restoration. Vegetation surveys of 1m x \ud 1m plots were conducted along previously-established transects of salt marshes for \ud four different sites; three restored salt marshes (Y-Marsh, Mitchell Marsh, Salmon \ud Creek Marsh) and one reference site (Reference Marsh). Additionally, vegetation data \ud were collected from three 20m x 50m modified Whittaker plots at each of the four \ud sites. Soil samples were collected at transect plots, processed according to National \ud Soil Survey Center protocol, and analyzed for pH, bulk density, salinity, conductivity, \ud and carbon/nitrogen content. Vegetation and soil characteristics (bulk density, \ud salinity, conductivity) were used to compare spatial patterns in vegetation diversity \ud for restored and reference salt marshes. Results indicate significant differences \ud \ud \ud \ud \ud \ud between the vegetation of reference and restored tidal marshes surveyed; differences \ud in vegetation were associated with differences in elevation, soil salinity, and \ud disturbance history. Outcomes indicate that restored marshes are more heterogeneous \ud in species composition. Marsh surface elevation does not differ significantly among \ud sites that were restored at different times in this estuary. The highest soil salinity and \ud lowest elevation occurs in Y-Marsh, the marsh closest geographically to the mouth of \ud the estuary. Vegetation of restored salt marshes is significantly less diverse and more \ud spatially homogeneous than that of reference sites, even four decades post-restoration. \ud Site hydrology, time since restoration, and prior land-use history influence the \ud vegetation community composition at Salmon River Estuary